This research project is concerned with the mechanism of steroid-induced alteration of growth pattern in human neoplastic cells of epithelioid type. The emphasis is being placed on the fluctuations of membrane-associated enzymes and on the modulating role of lipids in such changes. Steroids of the glucocorticoid series are assumed to activate a homeostatic mechanism which causes elevation of the model enzyme (alkaline phosphatase) in constitutively low cells and its suppression in constitutively high cells. This results in both types of strains in alteration of growth that resembles density-dependent growth inhibition. Specific biochemical changes that follow steroid-cell interaction include also accumulation of sialopeptides at the cell periphery and alteration of biosynthesis of membrane lipids including phospholipids and cholesterol. BIBLIOGRAPHIC REFERENCES: G. Melnykovych and M. L. Standaert: Choline incorporation into phospholipids by microsomal fractions from L5178Y lymphoma: Effects of prednisolone. Arch. Biochem. Biophys. 164:674-681, 1974. M. M. Standaert, S. L. Gray and G. Melnykovych: Growth characteristics of two HeLa S3 strains possessing low-level inducible and high-level suppressible alkaline phosphatase. Exptl. Cell Res. 94: 56-62, 1975.